Light-emitting diodes have typical forward voltages of 1.5 to 3.5 Volt. For being able to operate light-emitting diodes in electrical circuits with a greater service voltage, the light-emitting diodes must be protected against too high flowing currents. This protection can be performed in easy manner by semi-conductor components or resistances connected in series, which, however, may result in high power losses. Without high power losses, light-emitting diodes can be operated in electrical circuits with greater service voltages, by clocked inductances limiting the diode current. Clocked inductances of this type, however, require high circuit complexity and, therefore, are a complex and costly alternative.
For supplying the light-emitting diode with a corresponding service voltage, use of a PWM-control is known, as a rule with interposing smoothing elements, such as capacitors, as is outlined in FIG. 1 and is known, for example, from DE 100 13 207 or DE 41 41 059.
A number of circuit arrangements are known for operation with a 230 volt a.c. voltage, in which each light-emitting diode is respectively supplied with the correct phase via a full-wave rectifier circuit (see DE 23 04 620, JP 08137429, DE 200 02 482 U1, DE 100 54 212 A1).